STRUCTURE OF THE LUNGS OF REPTILES AND AMPHIBIA. 75 



In the fibrous stroma of the remaining parenchyma of the 

 lung, smooth muscular tissue is found, and frequently in such 

 abundance that it constitutes the greater portion of the whole 

 tissue. A thin layer of circular muscular fibres is found even 

 in the simple lung sacs of Tritons,* whilst in all lungs containing 

 alveoli, compact muscular fasciculi occur as the principal sup- 

 ports of the alveolar meshes, and of the septa, being especially 

 well developed at their thickened inner or free borders. 

 From these strong and compact principal bundles thinner 

 fasciculi are given off, and from these again a few isolated 

 muscular fibres are distributed on the flat base of the alveoli 

 near the internal surface. 



The nerves distributed to the lungs of Reptiles and Amphibia, 

 consisting of medullated and of non-medullated fibres, present 

 here and there small collections of ganglionic cells, which were 

 first closely examined by J. Arnoldf in the lungs of the Frog, 

 and were described by him as bell-shaped cells with granular 

 contents, on the concave surface of which a straight dark-edged 

 nerve fibre enters, the axis-cylinder of which terminates in the 

 nucleoli. According to Arnold, fine processes are given off 

 from the latter, running in a radial direction through the 

 nucleus, and continuous with a number of fine fibres that 

 traverse the granular contents of the cell, and ultimately enter 

 the so-called spiral fibre which forms a series of spiral coils 

 round the straight fibre. 



A capillary plexus, which lies flat on the alveolar walls, is 

 formed from the arterial trunks conveying venous blood to the 

 lungs ; its irregularly shaped rounded meshes do not exceed in 

 diameter the capillaries, which themselves correspond in dif- 

 ferent animals with the size of the blood-corpuscles. This respi- 

 ratory capillary plexus is distributed continuously over the lower 

 alveolar septa, whilst upon the summits of all the higher ridges, 



* From my own observations I am able to substantiate the statements 

 of H. Miiller (Wurzburgen naturwiss. Zeitschrift, Band ii., p. 131), in oppo- 

 sition to those of Reichert and Leydig, to the effect that a thin layer of 

 circular muscular fibres is present in the Triton toeniatus. 



t Virchow's Archiv, Band xxxviii., p. 431, 1863. Centralblatt fiir die 

 medicin. Wissenschaft., 1864, No. 42. Yirchow's Archiv, Band xxxii., 

 1864. 



